Solve 6x − 9 = 81

The solution of 6x − 9 = 81 is x = 15.

6x - 9 = 81\ \Rightarrow\ x = 15

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The lines y = 6x − 9 and y = 81 meet at x = 15. The solution of the equation is the x-coordinate of the point where the two sides are equal.

How to work it out

1
The goal is to get x alone. Undo the operations in the opposite order: first the subtraction, then the multiplication.
$6x - 9 = 81$
2
Add 9 to both sides:
$6x - 9 + 9 = 81 + 9 \ \Rightarrow\ 6x = 90$
3
Divide both sides by 6:
$\frac{6x}{6} = \frac{90}{6} \ \Rightarrow\ x = 15$
4
Check: put x = 15 back into the equation.
$6\cdot15 - 9 = 90 - 9 = 81 \checkmark$

LaTeX source of the formulas on this page

\[ 6x - 9 = 81\ \Rightarrow\ x = 15 \]
\[ 6x - 9 = 81 \]
\[ 6x - 9 + 9 = 81 + 9 \ \Rightarrow\ 6x = 90 \]
\[ \frac{6x}{6} = \frac{90}{6} \ \Rightarrow\ x = 15 \]
\[ 6\cdot15 - 9 = 90 - 9 = 81 \checkmark \]

Trying values of x in 6x − 9 = 81

x	6x − 9	Equals 81?
13	69	no
14	75	no
15	81	yes
16	87	no
17	93	no

Questions

What is x in 6x − 9 = 81?

The solution of 6x − 9 = 81 is x = 15.

How do you solve 6x − 9 = 81?

Add 9 to both sides to get 6x = 90, then divide both sides by 6 to get x = 15.

How do I check the answer?

Replace x by 15: 6(15) − 9 = 81, which is 81.

Solve 6x − 9 = 81

How to work it out

Trying values of x in 6x − 9 = 81

Questions

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